The present invention relates to a ceramic heater, and more particularly, it relates to a ceramic heater for use in manufacture or inspection processes of semiconductors.
As is well known, semiconductor products are of great importance and semiconductor chips as a typical example thereof are manufactured, for example, by preparing silicon wafers by slicing silicon single crystals to predetermined thickness and then forming various circuits on the silicon wafers.
The various circuits are formed into circuit patterns by sputtering or etching on silicon wafers and, since sputtering or etching is conducted at a high temperature and corrosive gases are sometimes used, they are preferably made of ceramic sintering products.
Such ceramic heaters comprise, as main constituent elements, a ceramic substrate and, a heat generation body disposed substantially over the entire rear face of the substrate, for example, a resistor pattern that generates heat upon current supply.
In existent ceramic heaters having such a constitution, it is preferred that insertion holes for lift pins for receiving and handing wafers (for example as disclosed in Japanese Patent Application Laid-open No. Hei 11-40330) or vacuum suction holes for heating the wafer in a state closely adhered to a heating surface are formed preferably, because the former is advantageous for conducting charge and discharge of wafers to and from the ceramic heater and the latter is advantageous for conducting rapid heating.
Further, since it is necessary for temperature control of the ceramic heater, recesses are disposed on the rear face of the ceramic heater for attaching temperature control parts such as thermocouple or thermal fuse and such temperature control parts are attached to the recesses.
However, the present inventors have found that the temperature becomes ununiform or lower temperature spots in which the temperature lowers locally are formed at the periphery of through holes such as the insertion holes or vacuum suction holes and in the recesses.
Such low temperature spots may possibly cause thermal shocks to the wafer upon heat-drying treatment. Further, the bottom of the recess is a portion in direct contact with the temperature control parts, for example, a temperature measuring element and, if the temperature is not uniform at the portion of the bottom, it is not preferred since the controllability of the temperature control part is lowered.
Further, a resin is sometimes coated on the wafer, which is exposed for development and thermally cured, but there was a problem that the cure of the resin was not uniform.
It is an object of the present invention to provide a ceramic heater capable of reducing the ununiformity of the temperature at the periphery of through holes such as insertion holes or vacuum suction holes thereby protecting the wafer against thermal shocks. Further, it is a subject of the present invention to provide a ceramic heater improved with the controllability for the temperature control parts such as thermocouples or thermal fuses.
A further object of the present invention is to provide a ceramic heater capable of uniformly curing resins.
The present inventors have made earnest studies for overcoming such problems and, as a result, have reached an idea that chamfering for the corner of the ceramic main body has an effect of improving ununiformity in the temperature distribution.
For dissolving the subject described above, a ceramic heater according to this invention has temperature control means on the surface or inside of a ceramic substrate in which at least a portion of corners of the ceramic substrate is chamfered.
In this case, it is preferred that the ceramic substrate has through holes and the corner of the through hole is chamfered. For example, it is preferred that a corner defined with the wall surface of the through hole and the surface of the ceramic substrate is chamfered.
In this case, the ceramic substrate preferably has a recess for containing a temperature control part on the side opposite to the heating surface, and the corner of the recess is chamfered. For example, it is preferred that the corner defined with the wall surface of the recess and the surface of the ceramic substrate and/or the corner defined with the bottom of the recess and the wall surface of the recess is chamfered.
In this case, it is preferred that the corner at the outer circumference of the ceramic substrate is chamfered at least on the side of the heating surface. For example, it is preferred that at least the corner defined with the outer circumferential lateral side of the ceramic substrate and the heating surface of the ceramic substrate is chamfered and/or the corner defined with the outer circumferential lateral side of the ceramic substrate and the lateral side of the ceramic substrate opposite to the heating surfaces is chamfered.
In this case, it is preferred that a groove is formed in the ceramic substrate and the corner of the groove is chamfered. For example, it is preferred that the corner defined with the upper surface and the groove wall surface of the groove and/or the corner defined with the bottom and the groove wall surface of the groove is chamfered.
The xe2x80x9ccornerxe2x80x9d includes (i) a corner defined with the heating surface or the surface opposite to the heating surface of the ceramic substrate and the outer circumferential lateral side of the ceramic substrate, (ii) a corner defined with a wall surface of a vacuum suction hole and a surface of the ceramic substrate in a case where the ceramic substrate has a such a vacuum suction hole for adsorbing and fixing a heated body placed on the main body, (iii) a corner defined with a wall surface of an insertion hole and surface of a ceramic substrate in a case where the ceramic substrate has such an insertion hole for lift pin for lifting a heated part, (iv) a corner defined with a wall surface of a recess and a surface of a ceramic substrate and/or a corner defined with a bottom surface of the recess and the wall surface of the recess in a case when the ceramic substrate has a recess for containing a temperature control part such as temperature measuring element (thermocouple, thermistor) or thermal fuse, which is appended to the heating means, and (v) a corner defined with an upper surface of a groove and a wall surface and a corner defined with the bottom surface of the groove and the wall surface of the groove in a case where the groove is formed on the surface of the ceramic substrate. In each of the corners, it is necessary at least the corner on the side of the heating surface or the side nearer to the heating surface is chamfered.
Further, while the corner on the side opposite to the heating surface has less thermal effect on the wafer but it is preferred that the corner on the side opposite to the heating surface is also chamfered.